1. Field of the Invention
The present invention relates to a method for increasing the charring ratio of coal, and more particularly, to a method for increasing the charring ratio of coal in the coal based ironmaking process using the coal.
2. Description of the Prior Art
Generally, the manufacturing apparatus of an ingot iron utilizing the known COREX process which is a smelting reduction process, suitable as a blast furnace substituting ironmaking process, can be largely classified into a melter-gasifier and a reduction shaft furnace. Ore passes through the reduction shaft furnace and then is fed into the melter-gasifier to produce the molten iron. The coal is fed into the melter-gasifier to play the role of iron ore reducing agent and fuel for melting the iron ore. When the coal is fed into the melter-gasifier at high temperature, moisture and volatile matter are volatilized at the same time with the feeding. The reduction gas gasified in the melter-gasifier reduces the iron ore in the reduction shaft furnace, while the char (fixed carbon and ash) from which the moisture and the volatile matter are removed, descends to the lower part of the melter-gasifier to finally reduce and melt the reduced iron ore. At this time, the generated amount of the volatile matter generated by the coal is determined by the condition of the melter-gasifier such as the temperature of the furnace, the pressure of the furnace, etc. However, in the commercialized COREX process for the present, about 10% or over of coke which nearly has the volatile matter, is used based on the total amount of the fed coal for securing the heat of the furnace along with the coal of which volatile matter is about 30% under a standard condition. Since 80-90% of the coke is carbon, the calorific value per unit volume of the coke becomes larger than that of the char of the coal which contains relatively less amount of the carbon, as the coke and the char move down to the lower part of the melter-gasifier. Accordingly, the coke is advantageous in securing the furnace heat. However, the use of the more expensive coke than the coal causes an increase of the cost of fuel. Therefore, the reduction in the amount of the coke utilized is required.
Meanwhile, Alan W. Scaroni in America reported his experimental result through a journal in 1981 that the volatile matter of the coal obtained under the condition which contents the proximate analysis of ASTM, can be changed by an additive admixed with the coal under the same condition.
According to his journal, the gasification of the coal can be maximized through the increase or decrease of the amount of the volatile matter volatilized at high temperature when an oxide (Al.sub.2 O.sub.3, Co--Mo--Al.sub.2 O.sub.3) pellet of 1 mm size, is added to the brown coal and the soft coal of minute powder (70-100 mesh).
It is known that when aluminum oxide (Al.sub.2 O.sub.3) is added, a secondary char is formed at the surface of a void present in the inner portion of the oxide to restrain the generation of the volatile matter. When Co--Mo--Al.sub.2 O.sub.3 is added, the generation of the volatile matter is accelerated by the acceleration of a gasifying reaction through the catalytic reaction of cobalt (Co). When considering the above-mentioned result, the method for increasing the charring ratio of the coal by restraining the generation of the volatile matter of the coal in the COREX process, can be accomplished by feeding a new material with the coal.
However, in the COREX process, since the additional new material should not largely affect slag while giving the above-described effect, the additive should be a similar component with the slag and a small amount thereof should be added so as not to largely affect the process.